What Are the Best Subject Lines for Email Marketing?
Last updated: 5 June 2025 — ⏱ 5 min read
Let’s face it. We’ve all judged an email by its subject line. Some shout for attention like a toddler in a toy store; others slink by unnoticed, doomed to the Promotions tab graveyard.
So what separates a “must-open” email from the digital equivalent of junk mail? Great subject lines. The kind that grab attention, spark curiosity, and make your subscribers actually excited to open your message.
Let’s dive into the best email subject lines, what makes them work, and how to craft your own.
Why Subject Lines Matter (Like, a Lot)
According to Mailchimp, 47% of email recipients decide whether to open an email based solely on the subject line. That’s almost half your audience making snap judgments faster than a bad Tinder swipe.
And you know what’s worse? 69% will report emails as spam just based on the subject line. Ouch.
In short: a great subject line = more opens = more eyeballs = more sales (or clicks, signups, dance party RSVPs… whatever your goal is).
So What Makes a Subject Line Work?
We've read loads of posts by experts from across the internet, including HubSpot, Wordstream, Salesforce, and Cognism, and distilled it all down so you don't have to. They all generally agree on a few universal truths:
✅ Keep it short and sweet
Mobile users dominate inboxes, and most phones chop off long lines like a machete in a jungle. Aim for 6–10 words or 40–50 characters max.
🔥 Example: “You left something behind…”
✅ Create curiosity (but don’t be clickbaity)
People love a mystery, as long as it delivers. Tease the content without revealing too much.
🔥 Example: “We need to talk…” (Juicy. Suspicious. Irresistible.)
✅ Use numbers and lists
Numbers signal structure, and make promises feel manageable.
🔥 Example: “5 things you didn’t know about SEO”
✅ Add personalization (but make it natural)
“Hi [First Name]” is basic and has been done, redone and overdone. Try adding location, preferences, or even recent behavior. Just be careful not to come across creepy.
🔥 Example: “Sarah, still interested in copywriting gigs?”
✅ Use urgency and scarcity (sparingly)
Nobody likes FOMO, but everyone responds to it. Just don’t overdo it or people will catch on. If you use this all the time, you can end up annoying people, who will then start to see all your emails as spammy.
🔥 Example: “⚠️ Ends tonight: Your 25% discount”
Real-World Subject Lines That Actually Work
Borrow a few of these proven winners.
| Subject Line | Why It Works |
|---|---|
| “Don’t open this email” | Reverse psychology — cheeky and clickable |
| “Your weekly dose of marketing magic 🪄” | Friendly + fun emoji = open-worthy |
| “You’re not going to like this…” | Creates tension and curiosity |
| “Last chance! (For real this time)” | Urgency with a wink |
| “Can we be honest for a sec?” | Personal and disarming |
More of these goldmines? OptinMonster has 101+ subject lines worth swiping.
Subject Line Sins: What Not to Do
Even the best intentions can go horribly wrong. Avoid these common pitfalls:
- ALL CAPS YELLING – Feels spammy, looks desperate.
- Excessive punctuation!!!!!! – One exclamation mark is enough. Really!!!
- Misleading bait-and-switch – People hate being tricked.
- Too vague – “Newsletter #17” tells me nothing.
- Over-personalization – “We saw you looking at red shoes at 2:14am” is unsettling.
- Too many emojis - 🚨📩 Email subject lines that have lots of emojis can instantly scream "SPAM"! 🤯📛
Tools to Help You Nail It
Not sure if your subject line slaps or flops? Try these tools:
Bonus tip: Run A/B tests. Test, restest and test again to make sure you're getting the most out of your email mnarketing. Even a small tweak, like moving a number to the front, can massively impact open rates. It's pretty standard these days for email marketing solutions to offer an A/B testing feature. Check out our posts comparing email marketing suites and exploring the best alternatives to mailchimp for a look at the best ones.
Need help choosing the right ESP for running those tests? See “Which Email Marketing Service Is the Best?” for our top 2025 picks.
TL;DR – The Cheat Sheet
- Shorter = better (aim for 6–10 words).
- Curiosity > clarity (but don’t mislead).
- Numbers, personalization, urgency = clicks.
- Test everything. Trust nothing.
- If in doubt, ask: Would I open this?
Final Word
Your subject line is your email’s handshake, pick-up line, and first impression, all rolled into one. Get it right, and your readers will lean in. Get it wrong, and your email’s spending the night in the spam folder.
So go ahead, get cheeky, be clever, and test test test. The inbox gods demand it.
Want help writing killer subject lines or testing your next campaign? Check out our reviews of moosend, getresponse, pabbly and systeme.io, which all include email marketing tools with subject line testing. Or just ask your friendly neighborhood AI.